In the production of clipboard, flake board, fiber board, and the like it is standard to compress a relatively thick mat by a factor of eight or more into a hard panel. The mat is soft and comprised of wood particles mixed with a phenolic or other binder. The finished workpiece is a hard board or panel with a pair of planar faces.
Such a panel is produced in a continuous press having a rigid press frame having vertically spaced upper and lower parts defining a press gap that can extend some 30 m. Upper and lower belts are spanned in the respective press parts between respective upstream and downstream rollers, at least one of which is driven to advance confronting upper and lower stretches of the lower and upper belts longitudinally through the press. Upper and lower press plates bear, typically by some sort of roller arrangement, on the lower and upper surfaces of the upper and lower stretches of the lower and upper belts. Normally arrays of rollers run between each belt and the respective supporting plate to reduce friction.
The two belts typically are braced at an intake mouth of the gap against flexible intake members or plates. The mouth flares upstream, from a width of more than 100 mm that is wide enough to easily receive the incoming mat down to a dimension somewhat greater than the finished width of the panel, between 10 mm and 20 mm. These intake members are flexible and are typically braced against the press frame by hydraulic cylinders that are hooked to a common controller so that the shape of the intake mouth can be set centrally. Such systems are described in German patent documents 195 18 879 and 197 40 325 as well as in U.S. Pat. No. 5,546,857.
The problem with these systems is that the shape of the intake mouth is generally fixed. It does not take into account conditions that might change during several hours of pressing, for instance a particularly hard or soft spot in the incoming mat. Thus it is possible for the belts to be damaged at the intake mouth. Similarly, resetting the shape of the intake mouth is a hit-or-miss proposition, normally dependent on the experience of the operator of the machine.